The Biology of Depression & Stress Pt. 2: Cortisol
(These are all of the posts we have on this topic)
5th Post on Stress and Depression: BDNF
6th Post on Stress and Depression: The Cholesterol/Dopamine Connection
7th Post on Stress and Depression: Increasing levels of Brain Derived Neurotrophic Factor (BDNF)
This blog post is the second in a series of posts that we will be doing on Depression & Stress.
In the previous entry (click here to see it), we discussed the fact that the current model for the treatment of depression revolves around one central theme. That theme is called the biogenic amine hypothesis. This theory views the cause of depression as a lack of key neurotransmitters (nor-epinephrine, serotonin & dopamine). The drugs currently being used to treat depression only focus on increasing these chemicals in the body, theoretically adding gas to a depressed person’s fuel tank.
This theory appears to be helpful in some people, but not all, in fact not even half. That is the purpose of this series of posts we are doing on depression, to look into other theories than just the standby concept.
Depression is clearly a physical problem. The lack of motivation, aches and pains, and increased general disease risks, make it clear that depression has roots deeper than just the emotions alone. Further these risks relate to an extended period of time. This means that there must be long-term factors that pre-dispose people to depression (no, we are not talking about inheriting depression from your parents).
A major factor predisposing people to depression is stress. Stress impacts the body through something called the Hypothalamic Pituitary Adrenal axis (HPA). The hypothalamus is the main regulator of all the hormones in the body. The hypothalamus releases something called corticotropin releasing hormone (CRH), and that goes down to your pituitary gland. Your pituitary gland is often called the “master gland” of the body. Your pituitary releases factors that influence all of your other glands: thyroid, adrenals, pancreas, sexual organs … you name it. The pituitary also releases something called Adrenocorticotropic hormone (ACTH). The name explains what it does: Adreno refers to the adrenals, cortico to cortisol and trophic means to stimulate. ACTH stimulates your adrenals to release cortisol, a major stress hormone.
The take way from this science is this: once your pituitary gland is stimulated to release CRH it starts a chain reaction of events that lead to increased stress hormone levels in the form of cortisol.
So … that’s it! Crush cortisol and we’re cool calm and collected … right?! Not so fast. Cortisol is vital to the human body. Without it, you’ll die. But, it should be available in short term and/or low grade doses, not the amounts that stimulate a fight or flight response. You need to moderate it.
The problem with chronic overstimulation of cortisol production is that it travels back into brain. The brain is very receptive to cortisol. It makes sense, since this hormone is designed to save us from hungry bears. However, the calm state of happiness that we all seek doesn’t fit well with running for your life. In fact, cortisol alters levels of serotonin dopamine and nor-epinephrine (please see our first post about these happy hormones). This is a cornerstone of the current thinking regarding what causes depression. But the root of the problem is not a lack of hormone; that is just a symptom. The REAL problem is the suppression of happy hormone production caused by stress.
How can cortisol be destructive? A seminal study done by Robert Sapolsky back in 1983 found that stress hormones cause brain damage. What he did to discover this was take rats and plant a placebo or a slow release form of cortisol in different sections of their brains. The area of the brain that he was studying was the hippocampus. The hippocampus has two functions that are vital to our discussion here: management of stress hormone levels and establishment of long-term memories. Guess what? The implanted stress hormones killed off a massive amount of cells in the brain in comparison to the placebo. What this tells us is that prolonged exposure to high levels of stress will kill your neurons and brain tissue. New evidence has emerged that supports this idea in humans. The average hippocampus of depressed people has been shown to be smaller than undepressed people by about 15%. It gives you something to think about regarding the loss of memory during traumatic events; it also shows how the poor regulation of stress can lead to brain dysfunction. They also feed each other … it’s a slippery slope in a lot of ways … if you lose hippocampal cells the lining on breaks go. Once the breaks go on your hippocampus, you can’t control the flood of stress hormones. These stress hormones further damage your hippocampus and the cycle continues.
This lends some scientific support to the idea that depression leads to other health problems. It’s long been known that excessive stress can lead to ill health. Now you can see that depression is just the end stage of excessive stress hormone production. The good news is that if you start taking steps to treat your depression, you can stop the wave of problems that come with depression.
In 2003, Yvette Sheline published a paper studying the function of the hippocampus in untreated people with depression. Take a look at the chart for people with untreated depression. But if you treat depression, Sheline found that it protected the hippocampus. This is very reassuring. If you treat depression, it saves your brain. This means that treating depression may be neuro-protective. It also means that toughing depression out and just living with it may be damaging your nervous system, and not something to be courageous about.
In this post we established the idea that stress is damaging your nervous system, and we gave you a direct link to how excessive stress may lead to depression. Further we’ve shown that when you start to put the break on depression, you can shortcut the cycle and may actually save your nerves and brain from further damage.
In our next post, we will go into ways that you can take action to reduce stress and protect yourself against the negative health consequences of depression.
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